Zinc(terpyridine)-Incorporated Metal–Organic Frameworks Enabled Photocatalytic Oxidative Coupling of Amines Under Visible Light in Atmospheric Air.

Poor light absorption ability severely limit the photocatalytic efficiency of metal–organic frameworks (MOFs) for chemical transformations. Herein, we have integrated the zinc(terpyridine) complex as "molecular antennas" into backbone of MOFs, to harvest visible light for aerobic oxidative coupling of amines. Two photoactive MOFs of Zn-CTP [CTP = (4′-(4-carboxyl)-terpyridine] and Zn-TPBA {TPBA = 4-([2,2′:6′,2′′-terpyridin]-4'-yl)benzoic acid} were thus prepared by employing the terpyridine-containing aromatic carboxylate ligands of CTP and TPBA as the organic linkers, respectively, to coordinate with zinc nitrate under solvothermal condition. Characterization results suggested the successful chelation of terpyridine with zinc(II) ions, giving zinc(terpyridine)-containing MOFs with high crystallinity. The incorporated zinc(terpyridine) complexes indeed acted as the "molecular antennas" in MOF to harvest visible light. Furthermore, π-conjugated terpyridine in organic linkers favored the charge transfer, leading to efficient charge separation in MOFs. Both zinc(terpyridine)-containing MOFs thus demonstrated high activities in the visible light-driven oxidation of amines to imines in air at room temperature. Particularly, extended π-conjugated linker of TPBA could further enhance the delocalization of conjugated electrons and optimize the electronic band structure that in favour of photocatalytic activity. As a result, Zn-TPBA enables almost quantitative oxidative coupling of benzylamine under visible light irradiation in atmospheric air, which was even more efficient than other reported photocatalysts in pure oxygen atmosphere. The salient advantages, such as operational simplicity, environmentally friendly, energy efficient, and high efficiency, made such photocatalytic system highly promising and practical in industrial application. Zinc(terpyridine) complex acted as "light antennas" in MOFs, making oxidative coupling of amines highly efficient under visible light in air. [ABSTRACT FROM AUTHOR]